1. Field of the Invention
This invention relates to a circuit device manufacturing method and particularly relates to a circuit device manufacturing method wherein plasma is irradiated onto a conductive foil to remove residues attached to the top surface of the conductive foil.
2. Description of the Related Art
Due to being employed in portable telephones, portable computers, etc., circuit devices that are set in electronic equipment have been demanded since priorly to be compact, thin, and lightweight. In order to meet such demands, semiconductor devices called CSP's (Chip Size Packages), which are equivalent or slightly larger in size to a chip, have been developed. However, with a general type of CSP, a supporting substrate, such as a glass epoxy substrate, ceramic substrate, etc., was required as an essential component for supporting the entire device. Since the supporting substrate is a thick member, the overall size of the semiconductor device tended to be large.
In view of the above problem, a circuit device, with which a supporting substrate is made unnecessary, has been developed. A method for manufacturing such a circuit device shall now be described.
As shown in FIG. 10(A), a conductive foil 100, formed of copper or other metal, is prepared and conductive patterns 100A are formed so as to realize predetermined electrical circuits. A known etching process using an etch resistant mask may be carried out as the method of forming separation grooves.
Referring to FIG. 10(B), circuit elements are affixed onto the top surfaces of conductive patterns 100A. As the circuit elements, chip elements 103, such as capacitors, resistors, etc., and semiconductor elements 102, etc., are affixed. Furthermore, the electrodes of semiconductor elements 102 are electrically connected to conductive patterns 100A via metal wires.
Referring to FIG. 10(C), covering by a sealing resin 105 is carried out. The circuit elements that were affixed in the prior step are covered and sealing resin 105 fills separation grooves 101 of conductive foil 100 as well.
Referring to FIG. 10(D), conductive foil 100 is etched from the rear surface and conductive foil 100 is thereby removed until the sealing resin 105 that fills separation grooves 101 becomes exposed. The respective conductive patterns 100A are thereby separated electrically. Forming of a solder resist, forming of external electrodes, etc., are then performed. Lastly, by dicing sealing resin 105 at locations indicated by the alternate long and short lines, the respective circuit devices are separated. A circuit device, which does not require a supporting substrate, was manufactured by processes such as the above.
As an art for removing contaminants attached to the top surfaces of patterns formed of metal, there is the art of plasma irradiation. A method of irradiating plasma onto a lead frame, on which a semiconductor element is mounted, to remove contaminants attached to the top surface shall now be described with reference to FIG. 11.
The configuration of a lead frame 110, which has been subject to a lead frame processing step, an element mounting step, etc., shall now be described with reference to FIG. 11(A). A semiconductor element 112 is mounted onto an island 114, which has been formed to a land form, and a plurality of leads 111 are disposed so as to surround island 114. Leads 111 correspond to electrodes provided on the top surface of semiconductor element 112 and the respective electrodes are electrically connected via metal wires 113 to leads 111.
The plasma irradiation step shall now be described with reference to FIG. 11(B). First, lead frame 110 is set in a sealed container. Gas is then introduced into the container and plasma gas is generated by a discharge. The top surface of lead frame 110 is cleaned by the collision of radicals or ions existing in the plasma gas with the top surface of lead frame 110.
However, with the above-described circuit device manufacturing method, there was the problem that the top surface of conductive foil 100 becomes contaminated due to the processes carried out prior to sealing by resin. Organic residues contained in the etchant used in the step of forming separation grooves 101, dust in the air, etc., are considered to be the contaminants. When sealing by sealing resin 105 is performed with such contaminants attached to the top surface of conductive foil 100, the force of attachment of sealing resin 105 to conductive foil 100 may decrease.
Also, with the method of cleaning a lead frame by plasma irradiation as shown in FIG. 11, since complex shapes are formed so as to form island 114 and leads 111, the plasma irradiation causes localized increases in electric potential to occur in lead frame 110. There was thus the problem of current flowing into semiconductor element 112 via metal wires 113 due to such localized potential differences in the lead frame and damaging a CMOS and other elements formed on the top surface of the semiconductor element. There was also the problem that, due to lead frame 110 becoming high in temperature in the plasma irradiation step, the leads become deformed and metal wires 113 become disconnected.
This embodiment of invention has been made in view of such problems and a main object of this embodiment of invention is to provide a circuit device manufacturing method, wherein cleaning and roughening of the top surface of a conductive foil is performed by irradiating plasma onto the top surface of the conductive foil. Another object of this embodiment of invention is to provide a circuit device manufacturing method that resolves the problems of breakage of a semiconductor element, etc., that occur in the process of removing contaminants attached to the top surfaces of conductive materials by use of plasma.